Archean cratons get a Hadean mash-up

The vast majority of the rock record over Earth's 4.6-billion-year history has been destroyed through subduction and recycling back into the mantle. Although some slivers of 4-billion-year-old crust remain in the rock record, only isolated zircon mineral grains are dated to be older. However, O'Neil and Carlson found isotopic evidence of reworked basaltic crust more than 4.3 billion years old mixed into some of the 2.7-billion-year-old rocks of the Superior Province in Canada. Thus, our planet's oldest crust was reworked and retained during formation of at least one continental craton.

Abstract

Geologic processing of Earth’s surface has removed most of the evidence concerning the nature of Earth’s first crust. One region of ancient crust is the Hudson Bay terrane of northeastern Canada, which is mainly composed of Neoarchean felsic crust and forms the nucleus of the Northeastern Superior Province. New data show these ~2.7-billion-year-old rocks to be the youngest to yield variability in neodymium-142 (142Nd), the decay product of short-lived samarium-146 (146Sm). Combined 146-147Sm-142-143Nd data reveal that this large block of Archean crust formed by reworking of much older (>4.2 billion-year-old) mafic crust over a 1.5-billion-year interval of early Earth history. Thus, unlike on modern Earth, mafic crust apparently could survive for more than 1 billion years to form an important source rock for Archean crustal genesis.